Environmental Engineering Reference
In-Depth Information
Table 3. Statistical significance of differences in bat activity between control and experimental trials
(*) denotes a significant result for both corrected P Bonferroni (P-values×number of comparisons)
and uncorrected P-values.
Antenna
Position
Index of
activity
Pulse
Length (μs)
Pulse Repetition
Rate (Hz)
Duty Cycle
(%)
n
t
p
P Bonfer-
roni
Rotating
Bat passes
0.08
2100
0.0168
20
1.89
0.07
0.22
Bat counts
0.08
2100
0.0168
20
1.50
0.15
0.45
FBR
0.08
2100
0.0168
20
1.80
0.08
0.26
Fixed
Bat passes
0.08
2100
0.0168
20
2.54
0.02*
0.06
Bat counts
0.08
2100
0.0168
20
2.87
0.01*
0.03*
FBR
0.08
2100
0.0168
20
3.82
0.001*
0.003*
Fixed
Bat passes
0.3
1200
0.036
18
3.69
0.002*
0.006*
Bat counts
0.3
1200
0.036
18
3.95
0.001*
0.003*
FBR
0.3
1200
0.036
18
6.78
< 0.001*
0.003*
doi: 1 0.1371 /journa l.pone.0006246.t003
Insect Abundance
Experimental trials were carried out during 32 nights from July, 2008 till September,
2008 representing a total of 32 hr of recording data within the following parameters:
1. Fixed antenna-pulse length/pulse repetition rate (0.08 μs/2100 Hz)-16 hr
2. Fixed antenna-pulse length/pulse repetition rate (0.3 μs/1200 Hz)-16 hr
A total of 10,430 insects were caught during 32 hr of sampling per trap. Ninety-
fi ve percent of the insects caught had wingspans <20 mm and were dried and included
in further analyses. Paired t tests revealed no signifi cant difference in insect abundance
between control and experimental traps when exposed to either a short (0.08 μs) or
medium pulse length (0.3 μs) radar signal (short pulse: n = 16, t = 1.50; P = 0.151; P
Bonferroni = 0.453; long pulse: n = 16, t = 1.89; P = 0.074; P Bonferroni = 0.222).
DISCUSSION
Currently there is no accepted method of successfully mitigating bat collisions with
wind turbines and attempts at deterring bats by the use of ultrasound have, as yet, been
unsuccessful. Therefore, the identification of alternative methods capable of inducing
an aversive response in bats approaching turbine blades is of paramount importance.
Very few field experiments have been carried out to ascertain the possible effects of
high frequency electromagnetic radiation on populations of wild animals. However,
studies have shown that electromagnetic radiation can influence the development, re-
production, and physiology of insects [33], mammals [34], and birds [35]. Our results
demonstrate that an electromagnetic signal from a small radar unit with a fixed anten-
na invariably reduced the foraging activity of bats within 30 m of the unit. However,
no significant decrease in activity was observed when the radar antenna was rotating.
This is not surprising; the length of time a bat would be exposed to the radar signal
is a function of the duty cycle of the radar signal (pulse length×pulse repetition rate)
and the dwell time (the duration of time that a target remains in the radar beam during
 
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